Geological Destination - Monument Valley Tribal Park

Back in November of 2019, while driving back from Arizona to the wife to do one of her Iron Man races, we drove through one of the Navajo Nation Tribal Parks, Monument Valley Tribal Park. As a runner, my wife wanted to get a shot of her running up the Forest Gump hill, while as a geologist, I just like looking at the pretty rocks.

Slightly downhill from us but essentially the same view in Forest Gump

As can be seen in the image, this is easily an icon geological location. The rock units within Monument Valley are essentially the same as the rock units within the nearby Canyon de Chelly National Monument, however the landscape is a bit different. Instead of the rocks being isolated within a canyon system like at the park, they are now elevated above the surrounding landscape. This is likely an effect of the Colorado Plateau, where this region had been slightly elevated compared to the areas further down south. A breakdown of the rock units within each of the mesas seen in the background is as follows:

Monument Valley geology. Image courtesy of the UGS.

The Shinarump, is part of the Chinle Formation, a Late Triassic (~225 million years old) yellow-grey river-deposited sandstone and conglomerate. 

Below the Shinarump is the Moenkopi formation. The Moenkopi Formation is an Early to Middle Triassic formation (~245 million years old) that is is predominantly made up of the reddish-brown shale. The Moenkopi was deposited within an intertidal environment, with alternating sea levels producing thinly bedded layers of mud (shale) and sand (sandstone). 

Below the Shinarump is the De Chelly Sandstone. The De Chelly Sandstone is a Permian age (~200 million years old) aeolian sandstone. Aeolian means that it is formed by blowing wind, in particular sand dunes, or a desert environment. When sand dunes are frozen in time, such as when they become rocks, and eroded you can see features termed cross-bedding. These rock preserve an ancient sand sea desert, known as an erg, that used to be located here. Sandstones are also frequently extremely hard rocks that are resistant to weathering. When they weather, they fracture into regular joints. Those are the vertical line patterns of the rocks as seen in the image above. It is also what produces the shear-walled rock mesas as we know them today. 

Below the De Chelly Sandstone, is the more erodible Organ Rock Shale. You can tell it erodes much more easily by the smooth slope that forms from the edge of the overlying sandstone. If the sandstone wasn't there to protect the shale, the shale would have eroded long ago. The Organ Rock Shale is another Permian formation (~270 million years old), that mainly comprised of mudstone (shale) and siltstones. They were deposited by streams within a tidal flat environment. The Organ Rock Shale then underlies much of the surrounding landscape which is then covered over with much, much younger (Quaternary) sediment (known as alluvium) transported in by winds and water from these and other surrounding rock formation.

Geological Destination - Ship Rock

Nearby to Four Corners Monument, and actually used during the original survey of the monument, is the monumental geological feature of Ship Rock. It is located in northwestern New Mexico, near the town of Ship Rock on the Navajo Nation. It is also known as Tsé Bit'a'í, or "the winged rock" in the native Navajo language.

View of Ship Rock from the south

Ship Rock is the volcanic remnant, or volcanic neck, of a prehistoric volcano that erupted ~30 million years ago. Ship Rock intruded within the much older Mancos Shale, a Cretaceous age (~90 million years old) formation made up of mostly claystone and siltstone with minimal amounts of sandstone and limestone that formed on the bottom of the Interior Cretaceous Seaway that once dominated the central portion of North America.

Geological map of Ship Rock, NM. Image courtesy of the NGMDB.

Part of the Navajo Volcanic Field, Ship Rock formed as what is known as a diatreme, a volcanic vent or pipe that was forced through flat-lying sedimentary rocks producing an expanded vent through explosive energy. The main portion of Ship Rock is composed of volcanic breccia, made up of a type of potassium-rich volcanic rock called "minette", which is thought to be formed from melting of the mantle. Ship Rock itself is ~1,600 feet wide at its widest and ~1,600 feet tall. When the volcano intruded into the Mancos Shale, it is thought that the current visible features were solidified ~2,500 to 3,300 feet below the surface of the Earth. However, the extreme weakness of the Mancos Shale has allowed extensive erosion to occur, carrying away the shale while leaving behind the much harder volcanic rock. 

View of Ship Rock from the south and the southern dike.

One of the more notable features of Ship Rock are the radiating features that emanate from the pinnacle itself. These were formed as volcanic features known as dikes. Dikes are vertical intrusions of magma into a surrounding bedrock. The vertical intrusion then hardens, leaving behind sheets of lava rock. Radiating outward from Ship Rock are six different dikes. These dikes can be seen on the geologic map above as red lines. However, due to the size of the southern dike and the distance to Ship Rock, I was only able to get a picture of the main southern dike.

View of the southern Ship Rock dike facing towards the south, away from Ship Rock.

View of the southern dike, facing towards the north, at Ship Rock

Closer up view of the southern dike.

It should be noted that Ship Rock is considered sacred to the Navajo, and while viewing the rock is allowed, climbing and hiking on the rock are prohibited.

A bit more of a distant view of Ship Rock. The two points on the right side of the photo are remnants of two of the smaller dikes that radiate out towards the northeast from Ship Rock.

On a recent trip to Canyon de Chelly National Monument, in the gift shop there was some additional information about Ship Rock and its Native origin story.

The story reads:

"Shiprock" 

(Naayee, Tse'bi taahi') 

Shiprock was once a Monster in our Navajo culture. Rock with wings (Naayee, tse'bi taahi') it was one of the most feared monsters of 10 different monsters in our Navajo Lure. If you look at it, a big piece of rock over 1000 feet was how tall the monster was. The Monster Shiprock would pick up people and drop them below into the jagged rocks and eat them. The Dine People feared him and the people wondered how these Monsters came to be. 

As the story goes, during this terrible time, the people (men and women) separated from each other causing conflict over who was going to be the leader. From there, they all went their separate ways. The men had problems without the help from the women and the women became promiscuous which resulted in deformed babies. They were ashamed of it, so they hid their babies. The deformed babies became Monsters. 

Changing Woman came to the rescue of the Dine. She too had babies (twins), one born for water and the other born for the sun. The twins asked their mother who their father was, finally she told them. And they began their plan to visit their father Sun, who helped them by forming them into humans. 

The Sun tested them to see if they were his real kids. Luckily, they passed all the tests given. As the end approached, their father asked why they came. The twins told him that there are many Monsters killing the Dine and they had come for weapons to kill the Monsters. 

The father Sun was worried and gave each twin a weapon and they came back down on a rainbow. The twins killed all the Monsters including the one Monster which is known today as Shiprock.

Drawing of the Monster which became Shiprock.

References
https://ngmdb.usgs.gov/mapview/?center=-108.755,36.663&zoom=12
https://geoinfo.nmt.edu/tour/landmarks/shiprock/home.html

https://www.nps.gov/articles/diatremes-and-maars.htm

http://volcano.oregonstate.edu/navajo-volcanic-field

Geological Destination - Four Corners Monument

Being located at the junction of four states, Four Corners Monument might just as well be considered a political park. However, geology is everywhere and therefore this is a perfect example of a geological park as well. The Four Corners Monument is a Navajo Tribal Park that designates the boundaries between the states of Utah, Arizona, Colorado, and New Mexico. It also designates the boundaries between the Navajo Nation and the Ute Mountain Ute Tribe Reservation. We visited the park on my birthday back in March of 2019. 

Me, laying across all four states at the monument. 

It has been said, by many people, that this point does not actually represent the point of intersection of the four states. These people are wrong. As noted by NOAA:

"... the Four Corners monument was established at the point he [surveyor Chandler Robbins] determined, to the very best of his ability and using the available technology, to be the prescribed location of 109 degrees 03 minutes West longitude and 37 degrees North latitude."

This precise location, however may be off by ~1,800 feet to the west of the monument. However, since this point was surveyed as the junction of the four states, and approved by the governments of the four states as well as the federal government, it IS the location of the junction, regardless of what the original intention of the surveyor may, or may not, have been.

It should also be noted that acclaimed geological landmark, nearby Ship Rock, was used as one of the marker locations for the designation of the Four Corners Monument. My next post will be on Ship Rock.

A closer look at the geodetic survey marker, designating the actual Four Corners point.

The Four Corners Monument sits within the Colorado Plateau. An area that is being forced upwards by the subducted Farallon Plate. 

Location of the Colorado Plateau. Image courtesy of Woodward, 1973.

Starting ~100 million years ago, along the west coast of North America was a subduction zone. This is where one plate goes beneath another plate. In this instance the Farallon Plate subducted, or went beneath, the North American Plate.

Graphic of the Farallon Subduction. Image courtesy of the NPS.

Over time the majority of the Farallon Plate was completely subducted, including the mid-ocean ridge (aka spreading center), leaving behind a new type of plate boundary along the coast of California. Instead of a subduction zone, there now was left a transform plate boundary, where one plate slides passed another one. This plate boundary is better known as the San Andreas Fault. Remnants of the Farallon Subduction Zone still exist along the coasts of northern California, Oregon, and Washington. 

Over the past ~10 million years, the subducted Farallon Plate was still a very hot plate, and therefore wanted to rise up underneath the North American Plate. Because of this, the Farallon Plate started to push upwards on North America, creating a region of the continent that is rising vertically upwards compared to the surrounding regions. This is the Colorado Plateau.

The geological features of the Colorado Plateau surrounding the Four Corners Monument. Image courtesy of Woodward, 1973.

The Colorado Plateau is made up of many of the world's most beautiful landscapes because of these geological forces playing around in the region. Looking specifically at the Four Corners region, anyone who has been to the Four Corners Monument will also notice that this area is a relatively flat, mountainless plain. This region is known as the Four Corners Platform. The platform is a relatively flat region that sits as an intermediary between adjacent basins and uplifts. In an area surrounded by mountains and canyons (and several anticlines (A-shaped bends in the rocks)) this region just happens to be in the middle of it all forming a flat surface. 

Geological Map of the Four Corners Monument. Image courtesy of NGMDB.

Looking at the rock units that cover the Four Corners Monument, they are represented on the map above by the symbols Jmw and Jmb, These are both members of the Upper Jurassic Age (~585 million years old) Morrison Formation. The Brushy Basin Member (Jmb), which covers the actual monument, is an interbedded green, purple, and grey mudstone and siltstone with grey and tan sandstone and conglomeratic sandstones. Known for its dinosaur fossils, the Brushy Basin Member was deposited from prehistoric rivers (fluvial) and lakes (lacustrine). The underlying Westwater Canyon Member (Jmw), is a yellowish-grey sandstone containing conglomeratic lenses and dark-reddish-brown siltstone. The Westwater Canyon Member is also a fluvial (river) deposited unit.

References

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544.8012&rep=rep1&type=pdf

https://www.ngs.noaa.gov/INFO/fourcorners.shtml

https://bluffutah.org/four-corners-monument

https://ngmdb.usgs.gov/mapview/?center=-108.996,36.967&zoom=10

https://ngmdb.usgs.gov/Prodesc/proddesc_4550.htm

https://www.sciencedirect.com/science/article/abs/pii/0037073889900705

https://sed.utah.edu/Morrison.htm

Geology of the National Parks Through Pictures - Canyon de Chelly NM

My next post about the Geology of the National Parks Through Pictures was from a rather snowy trip to Arizona where my wife ran an Ironman and then we did a tour of some of Arizona's National Parks, that unfortunately got snowed out towards the end of the trip.

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

Arizona State Geological symbols can also be found HERE.

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Canyon de Chelly National Monument
Our final park this trip, after a shortened visit to Petrified Forest and needing to skip another park entirely was Canyon de Chelly, which we ended up staying the night at the park hotel. Because of the snowstorm, the roads ended up being a bit hit or miss, with the lower elevation roads practically snowless and the higher elevation roads nearly impassable.

The entrance sign. The name of the canyon is a Spanish corruption of the Navajo word "Tsegi" meaning rock canyon. The pronunciation of "de Chelly" has slowly morphed over time from the Spanish "day shay-yee" to the modern day pronunciation of "d'SHAY". 

Canyon de Chelly is a unique park, since it is an actively lived in park. The park is run in conjunction with the Navajo Nation, where members of the Navajo Nation also live in the park and actively help preserve the ancient cliff dwellings within the walls of the canyon. The park is composed of several canyons, the primary two being Canyon de Chelly (the southern canyon with views from the road facing north) and the northern canyon, Canyon del Muerto, with views towards the south. The two canyons split off from each other towards the visitor's center.

When we arrived in the evening, we were advised to do the southern rim drive, along Canyon de Chelly, first. Then hold off and do the northern rim drive, along Canyon del Muerto, in the morning to get the best light in both. This is a view from Tunnel Overlook up the end of the Canyon de Chelly before the Canyon del Muerto splits off.

 A little bit further along the canyon, this is a view across the Canyon de Chelly from the Tsegi Overlook.

 View from the next stop at Junction Overlook. The canyon is made up almost entirely of one rock unit, the De Chelly Sandstone, which is a Permian age (~200 million years old) aeolian sandstone. Aeolian means that it is formed by blowing wind, in particular sand dunes, or a desert environment. When sand dunes are frozen in time, such as when they become rocks, and eroded you can see features termed cross-bedding. These rock preserve an ancient desert that used to be located here. We will look a little bit more into cross-bedding in a later photograph below.


A cross section of the Canyon de Chelly National Monument geology from the USGS. Although most of the canyon walls are composed of sandstone, there is a bit of the Triassic age Shinarump Conglomerate along the tops of the cliffs and the older Permian Organ Rock Formation along the base of the canyon.

View from the White House Overlook, looking down on the White House cliff dwelling. Many of the cliff dwellings on the southern side are not as easily seen from the road, however we can get a closer look at some of the later houses.

Here is the Face Rock overlook with the cliff dwellings located within the center of the cliff face in the center of the photograph.

A zoomed in view of the Face Rock cliff dwellings. These, and most of the cliff dwellings in the park, were built between 1100 and 1300 CE by the ancestral Puebloan people before the arrival of the modern day Navajo. This time period corresponds with other cliff dwellings in the region such as Mesa Verda and Tonto National Monument.

Along the Canyon del Muerto on the northern part of the park there are not as many overlooks but the views of the cliff dwellings are far better. This is the first stop along the northern rim at Antelope House Overlook with Antelope House below the cliff on the right part of the image.


Here is a closer up view of Antelope house. The buildings were constructed using a combination of the De Chelly Sandstone as building blocks and adobe bricks that were created from the mud and baked.

View from the Mummy Cave overlook. The cliff dwellings are located along the left side of the photo.


Close up view of the Mummy Cave cliff dwelling.

Yucca Cave cliff dwellings.

View up Canyon del Muerto at Massacre Cave Overlook.

View at the Massacre Cave Overlook with the cross-bedding in the De Chelly Sandstone highlighted by the snow. The cross-bedding is the angular lines through the sandstone layers. While here the layers of sandstone are generally horizontal, the cross-bedding is at an angle. The way cross bedding forms within a dune is illustrated below:


As sand is pushes up over a dune by the wind, the sand grains form parallel lines on the slipface of the dune. These parallel lines of the grains are what we see preserved within the rock. Image from Carleton.edu.

References

http://web.archive.org/web/20181001030919/https://3dparks.wr.usgs.gov/coloradoplateau/canyondechelly_strat.htm

http://web.archive.org/web/20170220180015/https://www.nature.nps.gov/Geology/parks/cach/index.cfm

http://npshistory.com/newsletters/sw_mon_rpt/special-report_no_20.pdf

https://serc.carleton.edu/NAGTWorkshops/sedimentary/images/cross_bedding.html